Illumination energy management in surface inspection

ABSTRACT

The disclosure is directed to a system and method of managing illumination energy applied to illuminated portions of a scanned wafer to mitigate illumination-induced damage without unnecessarily compromising SNR of an inspection system. The wafer may be rotated at a selected spin frequency for scanning wafer defects utilizing the inspection system. Illumination energy may be varied over at least one scanned region of the wafer as a function of radial distance of an illuminated portion from the center of the wafer and the selected spin frequency of the wafer. Illumination energy may be further applied constantly over one or more scanned regions of the wafer beyond a selected distance from the center of the wafer.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is related to and claims the benefit of theearliest available effective filing date(s) from the following listedapplication(s) (the “Related Applications”) (e.g., claims earliestavailable priority dates for other than provisional patent applicationsor claims benefits under 35 USC §119(e) for provisional patentapplications, for any and all parent, grandparent, great-grandparent,etc. applications of the Related Application(s)).

RELATED APPLICATIONS

For purposes of the USPTO extra-statutory requirements, the presentapplication constitutes a continuation patent application of UnitedStates Patent Application entitled ILLUMINATION ENERGY MANAGEMENT INSURFACE INSPECTION, naming Christian Wolters, Aleksey Petrenko, Kurt L.Haller, Juergen Reich, Zhiwei Xu, Stephen Biellak and George Kren asinventors, filed on Oct. 29, 2012, application Ser. No. 13/662,626.

TECHNICAL FIELD

The present disclosure generally relates to the field of inspectionsystems and more particularly to systems and methods of illuminationenergy management for inspection systems.

BACKGROUND

Inspection systems are often utilized in production and/or testing ofsemi-conductor devices. An inspection system may include an illuminationsystem configured to illuminate at least a portion of a semi-conductorwafer. The inspection system may scan for wafer defects or impurities bydetecting illumination reflected from the illuminated portion of thewafer. In some instances, illumination delivered to the illuminatedportion of the wafer may cause undesired thermal and/or photochemicaldamage to the wafer.

Reducing an energy level of illumination delivered to the illuminatedportion of the wafer may mitigate thermal/photochemical damage. However,reducing the energy level of illumination delivered to the illuminatedportion of the wafer may undesirably affect signal-to-noise ratio (SNR)of illumination detected by the inspection system, thereby limitingresolving power and/or accuracy of the inspection system. Accordingly,systems and methods of illumination energy management are desired tomitigate illumination-induced wafer damage while maintaining acceptableSNR of the inspection system.

SUMMARY

The present disclosure is directed to illumination energy management foran inspection system to mitigate thermal/photochemical damage caused byillumination utilized to scan at least a portion of a wafer surface.

In one aspect, the present disclosure is directed to a system formanaging illumination energy applied to a surface of a wafer. The systemmay include a sample stage configured to receive a wafer. The system mayfurther include a motor mechanically coupled to the sample stage. Themotor may be configured to actuate the sample stage to rotate the waferat a selected spin frequency. The system may further include anillumination system including at least one illumination sourceconfigured to provide illumination along an illumination path to asurface of a wafer. The illumination system may be configured toilluminate a first portion of the wafer with illumination having a firstenergy level. The illumination system further configured to illuminate asecond portion of the wafer with illumination having a second energylevel. At least one of the first energy level or the second energy levelmay be determined utilizing a radial distance of an illuminated portionof the wafer measured from the center of the wafer and the selected spinfrequency. For example, at least one of the first or second energylevels may be proportional to the radial distance of the illuminationportion of the wafer and the selected spin frequency (i.e. P∝(rf), whereP=energy level, r=radial distance, and f=spin frequency).

In another aspect, the present disclosure is directed to a method ofmanaging illumination energy applied to a surface of a wafer. The methodmay include the steps of: receiving a wafer; rotating the wafer at aselected spin frequency; illuminating a first portion of the wafer withillumination having a first energy level; and illuminating a secondportion of the wafer with illumination having a second energy level,wherein at least one of the first energy level or the second energylevel is determined utilizing a radial distance of an illuminatedportion of the wafer from the center of the wafer and the selected spinfrequency.

In another aspect, the present disclosure is directed to a method ofmanaging illumination energy applied to a surface of a wafer. The methodmay include the steps of: receiving a wafer; rotating the wafer at aselected spin frequency; illuminating a first portion of the wafer withillumination having a first energy level determined utilizing a firstradial distance of the first portion of the wafer from the center of thewafer and the selected spin frequency, wherein the first portion of thewafer is less than a selected radial distance from the center of thewafer; illuminating a second portion of the wafer with illuminationhaving a second energy level determined utilizing a second radialdistance of the second portion of the wafer from the center of the waferand the selected spin frequency, wherein the second portion of the waferis less than the selected radial distance from the center of the wafer;and illuminating a third portion of the wafer with illumination having athird energy level, wherein the third portion of the wafer is greaterthan the selected radial distance from the center of the wafer.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not necessarily restrictive of the present disclosure. Theaccompanying drawings, which are incorporated in and constitute a partof the specification, illustrate subject matter of the disclosure.Together, the descriptions and the drawings serve to explain theprinciples of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The numerous advantages of the disclosure may be better understood bythose skilled in the art by reference to the accompanying figures inwhich:

FIG. 1A is a block diagram illustrating an inspection system includingan illumination system for illuminating a portion of a wafer, inaccordance with an embodiment of this disclosure;

FIG. 1B is a block diagram illustrating the illumination system, whereinthe illumination system includes at least one electro-optical device formanaging an energy level of illumination delivered to the illuminatedportion of the wafer, in accordance with an embodiment of thisdisclosure;

FIG. 1C is a block diagram illustrating the illumination system, whereinthe illumination system includes at least one focusing element formanaging an energy level of illumination delivered to the illuminatedportion of the wafer, in accordance with an embodiment of thisdisclosure;

FIG. 1D is a block diagram illustrating the illumination system, whereinthe illumination system includes at least one waveplate and at least onepolarization element for managing an energy level of illuminationdelivered to the illuminated portion of the wafer, in accordance with anembodiment of this disclosure;

FIG. 1E is a conceptual view of a surface of the wafer illustrating afirst portion of the wafer having a first radial distance from thecenter of the wafer and at least one additional portion of the waferhaving at least one additional radial distance from the center of thewafer, in accordance with an embodiment of this disclosure;

FIG. 2 is a flow diagram illustrating a method of managing illuminationenergy applied to a surface of a wafer, in accordance with an embodimentof this disclosure; and

FIG. 3 is a flow diagram illustrating a method of managing illuminationenergy applied to a surface of a wafer, in accordance with an embodimentof this disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to the subject matter disclosed,which is illustrated in the accompanying drawings.

FIGS. 1 through 3 generally illustrate a system and method of managingillumination energy applied to a surface of a sample, such as asemi-conductor wafer. An inspection system may operate by scanningacross at least a portion of a surface of a wafer with illumination tolocate and/or analyze defects of the wafer. The wafer may be rotatedand/or translated to enable scanning across the substantial entirety ofthe wafer or across at least an annular or disk-shaped region of thewafer. Illumination-induced thermal and/or photochemical damage(hereinafter “damage”) may occur at inner regions of the wafer, sincevelocity of an illuminated portion of the wafer may decrease as scanningillumination approaches the center of the wafer. For example, anilluminated portion having a lower velocity may receive a higher dose ofillumination energy than an illuminated portion having a relativelyhigher velocity as a result of illumination applied to the lowervelocity illuminated portion for a longer time interval.

Wafer damage may be mitigated by decreasing an energy level ofillumination delivered to the illuminated portion of the wafer at innerregions of the wafer. However, decreasing the energy level ofillumination may undesirably affect signal-to-noise ratio (SNR) of theinspection system. Accordingly, the present disclosure provides a systemand method of managing illumination energy for an inspection system tomaintain acceptable SNR while mitigating damage caused by illuminationdelivered to the illuminated portion of the wafer.

As illustrated in FIG. 1A, an inspection system 100 may include anillumination system 102 configured to illuminate at least a portion of asurface of a wafer 112. The illumination system 102 may include at leastone illumination source 104 configured to deliver illumination to theilluminated portion of the wafer 112 along an illumination path. Theillumination path may include a direct line of sight from theillumination source 104 to the illuminated portion of the wafer 112.Alternatively, the illumination path may be delineated by one or moreoptical elements configured to direct illumination from the illuminationsource 104 along a selected path to the illuminated portion of the wafer112. For example, the illumination system 102 may include at least onefocusing lens 108 configured to focus illumination delivered to theilluminated portion of the wafer 112.

The inspection system 100 may further include at least one detector 110configured to receive at least a portion of reflected illumination fromthe illuminated portion of the wafer 112. The detector 110 may include aphotodiode, photodiode array, camera, or any other photo-detector knownto the art for detecting illumination. In one embodiment, the detector110 may be configured to receive reflected illumination from a detectionpath delineated by at least one optical element, such as a beam splitter106, configured to direct at least a portion of reflected illuminationfrom the illuminated portion of the wafer 112 along a selected path tothe detector 110.

The detector 110 may be communicatively coupled to at least computingsystem including at least one processor configured to execute programinstructions from carrier media, such as a HDD, SSD, flash memory,optical disc, magnetic disc, magnetic tape, RAM, or any other permanentor semi-permanent data storage. The computing system may be configuredto receive information (e.g. intensity, polarity, wavelength, etc.)associated with detected illumination from the detector 110. Thecomputing system may be further configured to determine defectcharacteristics (e.g. location, size, defect type, etc.) of the waferutilizing information associated with detected illumination.

In one embodiment, the inspection system 100 may be configured forscanning across at least one region of the wafer 112 to locate and/oranalyze wafer defects. The inspection system 100 may include a samplestage 114 configured to receive the wafer 112. The inspection system 100may further include one or more actuators 116 mechanically coupled tothe sample stage 114. For example, the actuator 116 may include a motorconfigured to rotate the wafer 112 at a selected spin frequency forscanning. In one embodiment, the actuator 116 may further include anactuation arm configured actuate the sample stage 114 sideways totranslate the scanned region of the rotated wafer 112 throughillumination delivered by the illumination system 102. The actuation armmay be further configured to actuate the sample stage towards and/oraway from the illumination system to adjust focus of illuminationdelivered to the illuminated portion of the wafer 112.

The foregoing embodiments are of an exemplary nature; however theinspection system 100 may include any combination of components and/orconfigurations known to the art, such as those described in U.S. Pat.No. 7,548,308, U.S. Pat. No. 6,271,916, and U.S. Pat. No. 6,201,601, allincorporation herein by reference. The inspection system 100 may furtherinclude one or more means for managing an energy level of illuminationdelivered to the illuminated portion of the wafer 112. Several means ofmanaging the energy level of illumination delivered to the illuminatedportion of the wafer 112 are known the art, such as systems and/ormethods described in U.S. Pat. No. 7,548,308, all incorporated herein byreference. For example the illumination system 102 may include one ormore filters configured to adjust illumination energy. Alternatively,the energy level of illumination delivered to the illuminated portion ofthe wafer 112 may be affected by varying the rotational speed of thewafer 112 utilizing the actuator 116 to adjust the selected spinfrequency of the sample stage 114. Several alternative means of managingillumination energy for the inspection system 100 are furtherillustrated by the following embodiments.

In one embodiment, the actuator 116 may be configured to translate thesample stage 114 relative to the illumination system 102 at a selectedspeed to control the scan pitch of illumination over the scanned regionof the wafer 112. The actuator 116 may be configured to control theenergy level of illumination delivered to illuminated portions of thewafer 112 by continuously varying the scan pitch. In another embodiment,the actuator 116 may be configured to actuate the sample stage 114relative to the illumination system 102 to affect focus of illuminationdelivered to the illuminated portion of the wafer 112. The actuator 116may be configured to control the energy level of illumination deliveredto illuminated portions of the wafer 112 by continuously varying thefocus level over the scanned region of the wafer 112.

In an embodiment, the illumination system 102 may include at least oneenergy controller, such as an opto-mechanical, electrical, and/orelectro-optical device, configured for controlling the energy level ofillumination delivered to the illuminated portion of the wafer 112. FIG.1B illustrates an exemplary embodiment of the illumination system 102,wherein the illumination system 102 may include at least oneelectro-optical device 120, such as a Pockels cell, disposed along theillumination path. The electro-optical device 120 may be configured toattenuate illumination received directly or indirectly from theillumination source 104 to control the energy level of illuminationdelivered to the illuminated portion of the wafer 112. Theelectro-optical device 120 may be configured to attenuate receivedillumination by a selected attenuation in response to an applied voltagesignal from a communicatively coupled voltage controller 122. Thevoltage controller 122 may be configured to continuously vary appliedvoltage to provide continuously varying attenuation of illuminationdelivered to illuminated portions of the wafer 112 over the scannedregion of the wafer. In a further embodiment, the illumination system102 may further include at least one attenuating optical element 124disposed along the illumination path in series with the electro-opticalillumination device 120. The attenuating optical element 124 may beconfigured to attenuate illumination received directly or indirectlyfrom the illumination source 104 by a fixed attenuation to allow abroader range of total attenuation.

In a further embodiment, the energy controller of the illuminationsystem 102 may be integrated within the illumination source 104. Forexample, the illumination source 104 may include a semi-conductor diodelaser driven by a variable current. The foregoing examples are includedfor illustrative purposes only. It is contemplated that any energycontroller for internally or externally controlling the energy level ofillumination emanating from the illumination source 104 may be utilizedto achieve the functionality described herein.

FIG. 1C illustrates another exemplary embodiment of the illuminationsystem 102, wherein the illumination system 102 may include at least onefocusing element 130 disposed along the illumination path. The focusingelement 130 may include at least one refractive element, such as aradially symmetric lens, a cylindrical lens, an astigmatic lens, ananamorphic prism pair, a multi-element lens assembly, and the like.Alternatively the focusing element 130 may include any other system ordevice known to the art for adjusting focus of illumination, such as azooming lens assembly. The focusing element 130 may be configured tocontrol the energy level of illumination delivered to the illuminationportion of the wafer 112 by varying spot size of delivered illumination.The focusing element 130 may be configured to vary spot size ofillumination delivered to illuminated portions of the wafer 112continuously over the scanned region of the wafer 112.

FIG. 1D illustrates yet another exemplary embodiment of the illuminationsystem 102, wherein the illumination system 102 may include at least onewaveplate 140, such as a half-wave plate, disposed along theillumination path in series with at least one polarization element 142,such as a polarizer or analyzer. The illumination system 102 may furtherinclude at least one motor mechanically coupled to the waveplate 140.The motor may be configured to rotate the waveplate 140 by a selectedrotation relative to the polarization element 142 to attenuateillumination directed along the illumination path through the waveplate140 and the polarization element 142 by a selected attenuation. Inanother embodiment, a motor may be mechanically coupled to thepolarization element 142. In either case, the illumination system 102may be configured to control the energy level of illumination deliveredto the illumination portion of the wafer 112 by rotating at least one ofthe wavepate 140 or the polarization element 142 to provide the selectedattenuation. Accordingly, the illumination system 102 may be configuredto continuously vary the energy level of illumination delivered toilluminated portions of the wafer 112 over the scanned region of thewafer 112.

The inspection system 100 may include one or more of the foregoing meansof managing illumination energy and/or any alternative means now orhereafter known to the art. A desired energy level of illuminationdelivered to the illuminated portion of the wafer 112 may be associatedwith a radial distance of the illuminated portion from the center of thewafer 112 and the selected spin frequency of the wafer 112. For examplethe desired energy level may be proportional to the radial distance ofthe illuminated portion and the selected spin frequency (i.e. P∝(rf),where P=energy level, r=radial distance, and f=spin frequency). Thedesired energy level may be further associated with a maximum energylevel of illumination that can be delivered to the illuminated portionof the wafer 112 without causing damage to the wafer 112 and tangentialspot size and radial spot size of illumination delivered to theilluminated portion of the wafer 112 (i.e. P∝P_(D)*S_(R)*S_(T), whereP_(D)=max energy level, S_(R)=radial spot size, and S_(T)=tangentialspot size).

The illumination system 102 may be configured to illuminate a pluralityof portions over the scanned region of the wafer 112 with illuminationhaving a plurality of desired energy levels. Accordingly, theillumination system 102 may be configured to mitigate wafer damage whilescanning across at least one region of the wafer 112 with acceptableSNR. In one embodiment, the illumination system 102 may be furtherconfigured for scanning across at least one region of the wafer at aconstant SNR by continuously adjusting energy level of illuminationdelivered to illuminated portions of the wafer 112. As illustrated inFIG. 1E, the illumination system 102 may be configured to illuminate afirst portion 152 of the wafer 112 with illumination having a firstenergy level, a second portion 154 of the wafer 112 with illuminationhaving a second energy level 156, a third portion of the wafer 112 withillumination having a third energy level, and so on. The energy level ofillumination delivered to illuminated portions of the wafer 112 at anygiven time may be further managed via the inspection system 100 or anyother means known to the art, in accordance with methods 200 and 300described herein.

FIG. 2 illustrates method 200 of managing illumination energy applied toilluminated portions of the surface of the wafer 112 being scanned bythe inspection system 100. At step 202, the sample stage 114 of theinspection system may receive the wafer 112. At step 204, the actuator116 may actuate the sample stage 114 to rotate the wafer 112 at theselected spin frequency for scanning by the inspection system 100. Atsteps 206 and 208, the illumination system 102 may illuminate scannedportions of the rotated wafer 112 with varying energy levels ofillumination across at least one scanned region of the surface of thewafer 112. For example, the illumination system 102 may illuminate afirst scanned portion 152 of the wafer 112 with illumination having afirst energy level at step 206, a second scanned portion 154 of thewafer 112 with illumination having a second energy level at step 208,and so on. In one embodiment, the illumination system 102 may varyillumination energy delivered to illuminated portions of the wafer 112in proportion to the radial distance of the illuminated portion from thecenter 150 of the wafer 112 and the selected spin frequency.

In an embodiment, the illumination system 102 may continuously vary theenergy level of illumination delivered to illuminated portions acrossone or more regions of the wafer 112. For example, the energy level ofillumination delivered across a region may be continuously ramped up ordown. Alternatively, the illumination system 102 may discretely vary theenergy level of illumination delivered to illuminated portions acrossone or more regions of the wafer 112. For example, the energy level ofillumination delivered across a region may be incrementally stepped upor down. Furthermore, the illumination system 102 may apply a hybridapproach to vary the energy level of illumination continuously over atleast one region and provide illumination at a constant energy level ora plurality of discrete energy levels over at least one additionalregion of the wafer 112.

FIG. 3 illustrates method 300 of managing illumination energy applied toilluminated portions of the surface of the wafer 112 by varying theenergy level of delivered illumination over at least one scanned regionincluding portions less than a selected radial distance λ from thecenter 150 of the wafer 112 and applying at least one selected energylevel of illumination over at least one additional scanned regionincluding portions greater than the selected radial distance λ from thecenter 150 of the wafer 112. At step 302, the sample stage 114 of theinspection system may receive the wafer 112. At step 304, the actuator116 may actuate the sample stage 114 to rotate the wafer 112 at theselected spin frequency for scanning by the inspection system 100. Atsteps 306 and 308, the illumination system 102 may illuminate scannedportions of the rotated wafer 112 less than the selected radial distanceλ from the center 150 with varying energy levels. For example, at step306, the illumination system 102 may illuminate a first scanned portion152 of the wafer 112 with illumination having a first energy leveldetermined as a function of the radial distance of the first portion 152from the center 150 and the selected spin frequency, wherein the firstportion 152 is less than the selected distance λ from the center 150 ofthe wafer 112. Similarly, at step 308, the illumination system 102 mayilluminate a second scanned portion 154 of the wafer 112 withillumination having a second energy level determined as a function ofthe radial distance of the second portion 154 from the center 150 andthe selected spin frequency, wherein the second portion 154 is less thanthe selected distance λ from the center 150 of the wafer 112, and so on.At step 310, the illumination system 102 may illuminate a third portion156 of the wafer 112 greater than the selected distance λ from thecenter 150 with illumination having a selected energy level, such as amaximum energy level or an energy level associated with a desired SNR.The illumination system 102 may similarly illuminate one or more scannedportions of the wafer 112 greater than the selected distance λ from thecenter 150 with illumination having the selected energy level. In oneembodiment, the illumination system 102 may accordingly provide varyingillumination energy over a first scanned region of the wafer 112 andconstant illumination energy over a second scanned region of the wafer112 to achieve desired sensitivity while mitigating wafer damage.

It is further contemplated that each of the embodiments of the methoddescribed above may include any other step(s) of any other method(s)described herein. In addition, each of the embodiments of the methoddescribed above may be performed by any of the systems described herein.

It should be recognized that the various steps described throughout thepresent disclosure may be carried out by a single computing system or,alternatively, a multiple computing system. Moreover, differentsubsystems of the system may include a computing system suitable forcarrying out at least a portion of the steps described above. Therefore,the above description should not be interpreted as a limitation on thepresent invention but merely an illustration. Further, the one or morecomputing systems may be configured to perform any other step(s) of anyof the method embodiments described herein.

The computing system may include, but is not limited to, a personalcomputing system, mainframe computing system, workstation, imagecomputer, parallel processor, or any other device known in the art. Ingeneral, the term “computing system” may be broadly defined to encompassany device having one or more processors, which execute instructionsfrom a memory medium.

Those having skill in the art will appreciate that there are variousvehicles by which processes and/or systems and/or other technologiesdescribed herein can be effected (e.g., hardware, software, and/orfirmware), and that the preferred vehicle will vary with the context inwhich the processes and/or systems and/or other technologies aredeployed. Program instructions implementing methods such as thosedescribed herein may be transmitted over or stored on carrier medium.The carrier medium may be a transmission medium such as a wire, cable,or wireless transmission link. The carrier medium may also include astorage medium such as a read-only memory, a random access memory, amagnetic or optical disk, or a magnetic tape.

All of the methods described herein may include storing results of oneor more steps of the method embodiments in a storage medium. The resultsmay include any of the results described herein and may be stored in anymanner known in the art. The storage medium may include any storagemedium described herein or any other suitable storage medium known inthe art. After the results have been stored, the results can be accessedin the storage medium and used by any of the method or systemembodiments described herein, formatted for display to a user, used byanother software module, method, or system, etc. Furthermore, theresults may be stored “permanently,” “semi-permanently,” temporarily, orfor some period of time. For example, the storage medium may be randomaccess memory (RAM), and the results may not necessarily persistindefinitely in the storage medium.

Although particular embodiments of this invention have been illustrated,it is apparent that various modifications and embodiments of theinvention may be made by those skilled in the art without departing fromthe scope and spirit of the foregoing disclosure. Accordingly, the scopeof the invention should be limited only by the claims appended hereto.

What is claimed is:
 1. A system for managing illumination energy appliedto a surface of a wafer, comprising: a sample stage configured toreceive a wafer; a motor mechanically coupled to the sample stage, themotor configured to actuate the sample stage to rotate the wafer at aselected spin frequency; and an illumination system configured toilluminate a first portion of the wafer with illumination having a firstenergy level, the illumination system further configured to illuminate asecond portion of the wafer with illumination having a second energylevel, wherein at least one of the first energy level or the secondenergy level is determined based on a selected radial distance and theselected spin frequency, a region associated with the selected radialdistance being larger than or equal to the first portion of the waferand the second portion of the wafer, wherein the second energy level isadjusted relative to the first energy level and relative to the selectedradial distance.
 2. The system of claim 1, wherein at least one of thefirst energy level or the second energy level is proportional to theselected radial distance of the illuminated portion of the wafer and theselected spin frequency.
 3. The system of claim 1, wherein theillumination system includes at least one energy controller configuredto attenuate an energy level of illumination delivered to theilluminated portion of the wafer by a selected attenuation, wherein theat least one energy controller includes at least one of anopto-mechanical device, an electrical device, or an electro-opticaldevice.
 4. The system of claim 3, wherein the at least one energycontroller includes a Pockets cell.
 5. The system of claim 3, whereinthe illumination system further includes at least one optical elementconfigured to attenuate the energy level of illumination delivered tothe illuminated portion of the wafer by a fixed attenuation.
 6. Thesystem of claim 1, wherein the illumination system includes at least onefocusing element configured to control spot size of illuminationdelivered to the illuminated portion of the wafer, wherein spot size isassociated with energy level of illumination delivered to theilluminated portion of the wafer.
 7. The system of claim 6, wherein theat least one focusing element includes at least one refractive element.8. The system of claim 7, wherein the at least one refractive elementincludes at least one of: a radially symmetric lens, a cylindrical lens,an astigmatic lens, an anamorphic prism pair, or a multi-element lensassembly.
 9. The system of claim 6, wherein the at least one focusingelement includes at least one zoom lens assembly.
 10. The system ofclaim 1, wherein the illumination system includes: a waveplate; apolarization element; and at least one motor mechanically coupled to atleast one of the waveplate or the polarization element, the at least onemotor configured to rotate at least one of the waveplate or thepolarization element to control an energy level of illumination directedthrough the waveplate and the polarization element to the illuminatedportion of the wafer.
 11. The system of claim 1, wherein the systemfurther includes: an actuation arm mechanically coupled to the samplestage, the actuation arm configured to actuate the sample stage relativeto the illumination system to control focus level of illuminationdelivered to the illuminated portion of the wafer, wherein focus levelis associated with an energy level of illumination delivered to theilluminated portion of the wafer.
 12. The system of claim 1, wherein thesystem further includes: an actuation arm mechanically coupled to thesample stage, the actuation arm configured to actuate the sample stagerelative to the illumination system to control scan pitch ofillumination delivered to the illuminated portion of the wafer, whereinscan pitch is associated with an energy level of illumination deliveredto the illuminated portion of the wafer.
 13. The system of claim 1,wherein the illumination system is further configured to: illuminate thefirst portion of the wafer with illumination having the first energylevel, wherein the first portion of the wafer is less than the selectedradial distance from the center of the wafer; illuminate the secondportion of the wafer with illumination having the second energy level,wherein the second portion of the wafer is less than the selected radialdistance from the center of the wafer; and illuminate a third portion ofthe wafer with illumination having a third energy level, wherein thethird portion of the wafer is greater than the selected radial distancefrom the center of the wafer.
 14. The system of claim 1, wherein thesecond energy level is adjusted relative to the first energy level tocompensate for at least one of a difference between a radial distance ofthe first portion and a radial distance of the second portion or aselected spin frequency of the first portion and a selected spinfrequency of the second portion.
 15. The system of claim 1, wherein atleast one of the first energy level or the second energy level isassociated with a maximum energy level or an energy level associatedwith a desired signal to noise ratio (SNR).
 16. The system of claim 1,wherein at least one of the first energy level or the second energylevel comprises an energy level that is continuously varied over aportion of the wafer.
 17. The system of claim 1, wherein at least one ofthe first energy level or the second energy level comprise a pluralityof discrete energy levels applied over a portion of the wafer.
 18. Amethod of managing illumination energy applied to a surface of a wafer,comprising: receiving a wafer; rotating the wafer at a selected spinfrequency; illuminating a first portion of the wafer with illuminationhaving a first energy level, the first portion being measured a firstradial distance from the center of the wafer; and illuminating a secondportion of the wafer with illumination having a second energy level, thesecond portion being measured a second radial distance from the centerof the wafer, wherein at least one of the first energy level or thesecond energy level is determined based on a selected radial distanceand the selected spin frequency, the selected radial distance of anilluminated portion of the wafer being measured from the center of thewafer, wherein a region associated with the selected radial distance islarger than or equal to the first portion of the wafer and the secondportion of the wafer, and wherein the second energy level is adjustedrelative to the first energy level and relative to the selected radialdistance.
 19. The method of claim 18, wherein at least one of the firstenergy level or the second energy level is proportional to the selectedradial distance of the illuminated portion of the wafer and the selectedspin frequency.
 20. The method of claim 18, wherein the method furtherincludes: attenuating an energy level of illumination delivered to atleast one of the first illuminated portion or the second illuminatedportion of the wafer by a selected attenuation.
 21. The method of claim20, wherein the method further includes: attenuating the energy level ofillumination delivered to at least one of the first illuminated portionof the wafer or the second illuminated portion by a fixed attenuation.22. The method of claim 18, wherein the method further includes:controlling spot size of illumination delivered to at least one of thefirst illuminated portion or the second illuminated portion of thewafer, wherein spot size is associated with energy level of illuminationdelivered to the respective illuminated portion of the wafer.
 23. Themethod of claim 18, wherein the method further includes: directingillumination through a waveplate and a polarization element to theilluminated portion of the wafer; and rotating at least one of thewaveplate or the polarization element to control an energy level ofillumination delivered to at least one of the first illuminated portionor the second illuminated portion of the wafer.
 24. The method of claim18, wherein the method further includes: disposing the wafer on a samplestage; and actuating the sample stage relative to an illumination systemto control focus level of illumination delivered from the illuminationsystem to at least one of the first illuminated portion or the secondilluminated portion of the wafer, wherein focus level is associated withan energy level of illumination delivered to the respective illuminatedportion of the wafer.
 25. The method of claim 18, wherein the methodfurther includes: disposing the wafer on a sample stage; and actuatingthe sample stage relative to an illumination system to control scanpitch of illumination delivered from the illumination system to at leastone of the first illuminated portion or the second illuminated portionof the wafer, wherein scan pitch is associated with an energy level ofillumination delivered to the respective illuminated portion of thewafer.
 26. The method of claim 18, wherein the second energy level isadjusted relative to the first energy level to compensate for at leastone of a difference between a first radial distance of the first portionand a second radial distance of the second portion or a selected spinfrequency of the first portion and a selected spin frequency of thesecond portion.